In an experiment, a small steel ball falls through a liquid at a constant speed of $10 \mathrm{cm}/\mathrm{s}$. If the steel ball is pulled upward with a force equal to twice its effective weight, how fast will it move upward?

$\begin{array}{l}\text{ Weight of the body }\\ \text{W}=\text{mg}=\frac{4}{3}\pi {\text{r}}^3\rho \text{g}\\ \text{T}=\frac{4}{3}\pi {\text{r}}^3\sigma \text{g}\\ \text{ and F}=6\pi \eta \text{vr}\\ \text{ When the body attains terminal velocity net force acting }\\ \text{ on the body is zero. i.e., W}-\text{T}-\text{F}=0\\ \text{ And terminal velocity v}=\frac{2}{9}\frac{{\text{r}}^2(\rho -\sigma )\text{g}}{\eta }\\ \text{ As in case of upward motion upward force is twice its }\\ \text{ effective weight, therefore, it will move with same speed }\\ 10 \text{cm}/\text{s}.\end{array}$